This refers to the whole day. The writer speaks of the whole day as if it were these two parts. In the Jewish culture, a day begins when the sun sets. See how you translated this in [Genesis 1:5](./05.md). (See: [[rc://en/ta/man/translate/figs-merism]])
This refers to the fifth day that the universe existed. See how you translated "the first day" in [Genesis 1:5](./05.md) and decide if you should translate this the same way.